Modem apparatus, communication apparatus and communication control method

ABSTRACT

The present invention calculates a product of the present sampling data by the sampling data 1 data unit ahead through multiplier  14 , adds up product values calculated for every sampling by going back to the time point 1 data unit ahead through adder  16  and detects a reference timing with regard to a CP signal using the addition value.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a modem apparatus using an XDSLtechnology that allows high-speed communications of several M bits/seceven with a telephone copper wire cable, and more particularly, to amodem apparatus, communication apparatus and communication controlmethod that detect a CP (Cyclic Prefix) signal added to every data unit(a predetermined number of samples) of initializing signals.

[0003] 2. Description of the Related Art

[0004] Against a background of the widespread proliferation of theInternet, there is a growing demand for high-speed access channelsavailable for constant connection of the Internet. Furthermore, opticalfibers are increasingly introducing forbackbone of carriers and use ofultra high-speed channels of giga-bit class is beginning in their coresections. On the other hand, most of subscriber channels connecting userresidences and a carrier station are copper wire cables installed fortelephones. Therefore, the introduction of an XDSL technology, whichallows high-speed communications of several M bits/sec with telephonecopper wire cables, is under study.

[0005] One of the XDSL technologies is an ADSL system. The ADSL systemuses carrier frequencies in a band of 35 kHz or higher, which is by farhigher than the band used for telephones (4 kHz or below). For thisreason, the ADSL system has an advantage of using telephone lines tocarry out high-speed data communications without impairment of thetelephone functions.

[0006] A voice modem using a band of 4 kHz or below sends a trainingsignal prior to data transmission and then sends a data signal. An ADSLmodem sends an initializing signal, which is equivalent to the trainingsignal, and then sends a data signal.

[0007]FIG. 7 shows a sequence diagram of an initializing signal sent bythe ADSL modem. As shown in FIG. 7, the initializing signal has a CPsignal added at the beginning of every data unit (256 samples in thecase of G.Lite) starting at some midpoint of the signal. The CP signalis configured by the same data as that of a predetermined number ofsamples (16 samples in the case of G.Lite) of the rear end of the dataunit. That is, the 16 samples of the rear end of the data unit arecopied and added at the beginning of the data unit, forming a unit of272 samples (256+16) as a whole. Adding this CP signal at the beginningof every data unit also when a data signal is sent will preventinter-code interference between data units. This also makes it possibleto precisely demodulate a DMT (Discrete Multi Tone) modulated signaladopted by the ADSL system.

[0008] However, regardless of high-speed communication based on the ADSLsystem, the reception terminal cannot determine from which part of theinitializing signal a cyclic insertion of the CP signal starts. For thisreason, it is difficult to directly recognize the boundary between theCP signal and signal body. Here, the cyclic insertion refers to addingthe rear 16 samples of the data unit at the beginning of the relevantdata unit and repeating this procedure for every data unit.

SUMMARY OF THE INVENTION

[0009] It is an object of the present invention to provide a modemapparatus, communication apparatus and communication control methodcapable of accurately detecting a CP signal sent at some midpoint of aninitializing signal without any detection error and preciselydemodulating a DMT-modulated signal.

[0010] The present invention calculates a product of present samplingdata by sampling data, one data unit ahead, and retroactively adds upproduct values calculated for every sampling by going back to the timepoint 1 data unit ahead. The present invention then detects a referencetiming with regard to a CP signal using the addition value.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The above and other objects and features of the invention willappear more fully hereinafter from a consideration of the followingdescription taken in connection with the accompanying drawing whereinone example is illustrated by way of example, in which;

[0012]FIG. 1 is a functional block diagram of a reception system of amodem apparatus according to an embodiment of the present invention;

[0013]FIG. 2 illustrates a connection mode according to an ADSL system;

[0014]FIG. 3 illustrates an initialization sequence based on G.992.2;

[0015]FIG. 4 illustrates an extract of a portion of an initializationsignal including parts before and after a segue signal;

[0016]FIG. 5 illustrates a relationship between a data pattern of areverb signal and segue signal and adder output;

[0017]FIG. 6 is a flow chart to detect a reference timing of CPdetection in the modem apparatus according to the embodiment above; and

[0018]FIG. 7 is a data sequence diagram of an initializing signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] With reference now to the attached drawings, an embodiment of thepresent invention will be explained in detail below.

[0020]FIG. 1 is a functional block diagram of a reception system of amodem apparatus according to an embodiment of the present invention andis an excerpt of the part that detects a reference timing to ascertainthe position of a CP signal in an initializing signal. Before explainingthe configuration of the part corresponding to reference timingdetection to ascertain the CP position, an example of the channelconnection mode constructed via this modem apparatus will be brieflyexplained with reference to FIG. 2.

[0021] A telephone station serving as a carrier station and a subscriberresidence, a user residence, are connected via copper wire cable 21. Atthe subscriber residence, telephone set 23 and ADSL terminal sideapparatus 24 are connected via splitter 22. Furthermore, personalcomputer 26 as a communication terminal apparatus is connected to ADSLterminal side apparatus 24 via a local network such as 10-BASE-T. At thetelephone station, exchange 28 and hub (or router) 29 are connected viaADSL station side apparatus 27.

[0022] When communication terminal apparatus 26 carries out a datacommunication, an initializing signal is sent/received between ADSLterminal side apparatus 24 and ADSL station side apparatus 27 at thetelephone station. This embodiment will be explained assuming that thismodem apparatus is mounted on ADSL terminal side apparatus 24 at thesubscriber residence, but the modem apparatus can also be mounted onADSL station side apparatus 27. Splitter 22 can be incorporated in ADSLterminal side apparatus 24 and no splitter is required in the case ofG.Lite.

[0023] In FIG. 1, AD converter 11 samples a reception signal sent viacopper wire cable 21 and outputs the sampling data to auto gaincontroller 12. The sample data with gain adjusted by auto gaincontroller 12 is input to first shift register 13 and multiplier 14 inparallel.

[0024] First shift register 13 has a register length equivalent to thenumber of samples of 1 data unit. That is, in the case of G.Lite, firstshift register 13 is configured by 256 delay elements. When certainsample data is input, first shift register 13 outputs the sample data256 samples ahead to multiplier 14. Therefore, multiplier 14 calculatesa product of the sample data input this time by the sample data 1 dataunit ahead (256 samples ahead in the case of G.Lite). The product valueoutput from multiplier 14 is assigned a polarity and input to secondshift register 15.

[0025] Second shift register 15 has the same register length as that offirst shift register 13 and has a structure having a tap to extractstored data from each delay element. Therefore, products of 256 samplesfrom the present sample to the one 256 samples ahead by 256 samples fromthis sample to the sample 256 samples ahead with polarities assignedrespectively are output in parallel to second shift register 15.

[0026] Adder 16 adds up the 256 product values with polarities stored insecond shift register 15. This addition value is input to minimum valuedetermination circuit 17. Minimum value determination circuit 17 detectsthe position at which the time series data string made up of theaddition values output from adder 16 reaches a minimum value as areference timing and outputs a minimum value detected signal. As will bedescribed later, the minimum value detected signal will indicate theposition of the boundary between a first symbol and second symbol of thesegue signal and the position 9 symbols later from there (256 samples×9)is the position of the beginning of the CP signal.

[0027] Here, an algorithm for detecting a reference timing used toascertain the CP position from an initializing signal will be explained.

[0028]FIG. 3 illustrates an initialization sequence according to G.Lite(G.992.2). The ADSL station side apparatus installed at the stationsends 10 symbols of segue signal (C-SEQUE1) after sending 1024 symbolsof reverb signal (C-REVERB3) in the initialization sequence.Furthermore, after sending 10 symbols of segue signal (C-SEQUE1),addition of a CP signal is started from the immediately followingtransmission signal. In the same way, the ADSL terminal side apparatusinstalled at the subscriber residence sends 1024 to 1056 symbols ofreverb signal (R-REVERB2) and then sends 10 symbols of segue signal(R-SEGUE1) in the initialization sequence. Furthermore, after sending 10symbols of segue signal (R-SEGUE1), addition of a CP signal is startedfrom the immediately following transmission signal.

[0029]FIG. 4 shows the initialization sequence of the ADSL station sideapparatus and shows symbol series of a section where a reverb signal(C-REVERB3) is changed to a segue signal (C-SEGUE1) and a section wherea segue signal (C-SEGUE1) is changed to the following transmissionsignal.

[0030] In the case of G.Lite (G.992.2), 1 data unit (signal body)corresponding to 1 symbol of both the reverb signal and segue signal isconfigured by 256 data items. The reverb signal (C-REVERB3) repeats 256data patterns for 1024 symbols and the segue signal (C-SEGUE1) repeats256 data patterns for 10 symbols.

[0031] The reverb signal is the following signal defined in ITU-TG.992.2 or G.992.1. As a data string that forms a data streamcorresponding to 1 symbol, the following pseudo-random sequence isgenerated.

[0032] In the case of upstream:

[0033] dn=1 for n=1 to 6

[0034] dn=dn−5 EXOR dn−6 (modulo2) for n=7 onward

[0035] In the case of downstream:

[0036] dn=1 for n=1 to 9

[0037] dn=dn−4 EXOR dn−9 (modulo2) for n=10 onward

[0038] The above sequence is divided every 2 bits and allocated on acomplex plane expressed by X and Y axes as follows. The “EXOR” abovedenotes an exclusive OR.

[0039] 00→X+ Y+

[0040] 01→X+ Y−

[0041] 11→X− Y−

[0042] 10→X— Y+

[0043] Suppose a sequence of 128 or 256 complex numbers allocated on thecomplex plane is:

[0044] Z1Z2 . . . Zm

[0045] where the first of the complex sequence is 00 and the portioncalled a “pilot tone” is (X+Y+).

[0046] Furthermore, an inverse Fourier transform is applied to asequence that links the above complex sequence with a complex sequencethat constitutes Hermitian symmetry with respect to the relevant complexsequence:

[0047] Z1Z2 . . . Zm Conjugate of Zm . . . conjugate of conjugate Z1 ofZ2

[0048] The 256 real number components of this inverse Fourier transformresult constitute a reverb signal.

[0049] The segue signal is formed as follows: The above reverb signal isrotated 180 degrees on the complex plane except 00 on the complex planeand the position X+ Y+called a “pilot tone” and the following complexsequence is obtained:

[0050] Z1Z2 . . . Zm

[0051] Hermitian symmetry with this is taken as follows:

[0052] Z1Z2 . . . Zm Conjugate of Zm . . . conjugate of conjugate Z1 ofZ2

[0053] And this is subjected to an inverse Fourier transform. The 256real number components of this inverse Fourier transform resultconstitute a segue signal.

[0054] The reverb signal and segue signal generated according to theabove rule are signals with phases mutually inverted by virtually 180degrees. FIG. 5 shows that the reverb signal and segue signal havephases mutually inverted by virtually 180 degrees. The curve describedin correspondence in time with the reverb signal and segue signal inFIG. 5 represents addition values with polarities output from adder 16at different sample time points. As shown in FIG. 5, the phases of thelast symbol (1024th symbol) of the reverb signal and the first symbol(1st symbol) of the segue signal are opposite over 1 entire symbol. Forthis reason, at the reception terminal, individual sample data itemsforming the first symbol of the segue signal and the sample data(individual sample data items forming a reverb signal) 1 data unit (256samples) ahead from each sample time point have opposite polarities.Therefore, the product of the present sample data by the sample data 1data unit ahead in the above positional relationship always shows anegative polarity. In the period of each sample data item during whichthe present sample data forms the 1st symbol of the segue signal, eachproduct value has a negative polarity. Therefore, adding product valuescorresponding to the past 1 data unit (256 samples) to the individualsample data items that form the 1st symbol of the segue signal shows aminimum value as shown in FIG. 5.

[0055] This embodiment detects a minimum value from the time series dataof addition values output from adder 16. As shown in FIG. 4 and FIG. 5,since the position at which the above minimum value is detected is 9symbols (256×9) after the position of the beginning of the CP signal,once the position of the minimum value above is detected, the positionat which the CP signal starts can be identified using that position as areference timing.

[0056]FIG. 1 shows the hardware circuit to detect a reference timingwith regard to the CP signal in the modem apparatus above, but it ispossible to execute the processing from AD converter 11 onward bysoftware. FIG. 6 is a flow chart to execute CP detection processing inthe modem apparatus above.

[0057] At a sampling time (S61), 1 sample is input (S62) and a productof the sample data this time by sample data 1 data unit ahead iscalculated with a polarity (S63). Then, product values for 256 samplescorresponding to the past 1 data unit with polarities are added (S64).Then, it is determined whether the addition value this time is a minimumvalue or not (S65). An algorithm for determining a minimum value is notparticularly limited.

[0058] The sampling number at the position at which the minimum value isdetected in step S65 is recorded (S66) and the CP signal position isidentified from the recorded sampling number (S67). After the CP signalposition is identified, the data unit of the data signal sent after theinitializing signal is extracted and demodulated with reference to theCP signal added at the beginning of the data unit.

[0059] In the connection mode shown in FIG. 2, ADSL terminal sideapparatus 24 is connected to communication terminal apparatus 26 vialocal network 25, but it is also possible to use a mode in whichcommunication terminal apparatus 26 incorporates ADSL terminal sideapparatus 24. Furthermore, communication terminal apparatus 26 is notlimited to a personal computer, but can be any other apparatus equippedwith a facsimile apparatus (including Internet fax) and a communicationfunction.

[0060] The present invention described above can provide a modemapparatus, communication apparatus and communication control methodcapable of accurately detecting a CP signal sent at some midpoint of theinitializing signal without any detection error and preciselydemodulating a DMT-modulated signal.

[0061] The present invention is not limited to the above-describedembodiments, and various variations and modifications may be possiblewithout departing from the scope of the present invention.

[0062] This application is based on the Japanese Patent Application2000-094257 filed on Mar. 30, 2000, entire content of which is expresslyincorporated by reference herein.

What is claimed is:
 1. A modem apparatus comprising: a sampling sectionthat samples a reception signal; a multiplier that calculates a productof the present sampling data by the sampling data 1 data unit ahead; anadder that adds up product values calculated for every sampling by goingback to the time point 1 data unit ahead; and a detector that detects areference timing with regard to a CP signal using the addition valuecalculated by said adder.
 2. The modem apparatus according to claim 1 ,wherein said detector detects a minimum value from the time series dataof said addition value and recognizes the sampling timing correspondingto the detected minimum value as said reference timing.
 3. The modemapparatus according to claim 1 , wherein said detector detects asampling timing at which the sum total of products of each sampling dataitem corresponding to the final symbol of a reverb signal sent in aninitializing signal by each sampling data item corresponding to thefirst symbol of a segue signal sent following said reverb signal isoutput as said reference timing.
 4. The modem apparatus according toclaim 2 , wherein the position 9 symbols ahead of the sampling timingcorresponding to said minimum value is recognized as the beginning ofthe CP signal.
 5. An ADSL terminal side apparatus equipped with themodem apparatus according to claim 1 .
 6. An ADSL station side apparatusequipped with the modem apparatus according to claim 1 .
 7. Acommunication apparatus equipped with the modem apparatus according toclaim 1 .
 8. A communication control method comprising sampling areception signal; calculating a product of the present sampling data bythe sampling data 1 data unit ahead; adding up product values calculatedfor every sampling by going back to the time point 1 data unit ahead;and detecting a reference timing with regard to a CP signal using saidaddition value.
 9. The communication control method according to claim 8, wherein a minimum value is detected from the time series data of saidaddition value and the sampling timing corresponding to the detectedminimum value is recognized as said reference timing.
 10. Thecommunication control method according to claim 8 , wherein a samplingtiming at which the sum total of products of each sampling data itemcorresponding to the final symbol of a reverb signal sent in aninitializing signal by each sampling data item corresponding to thefirst symbol of a segue signal sent following said reverb signal isoutput is detected as said reference timing.